1. Field of the Invention
A subject of the present invention is a fast-action make-and-break switch. Fast-action make-and-break switches are switches in which the current is cut quickly, as opposed to switches in which the separation of electrical contacts is slow and depends on the speed of manual action of an operator. The switch of the invention is more particularly a switch of the end-of-travel type, for which the fitting and therefore usage tolerances are improved. What happens is that, according to the invention, the user has available to him, for an end-of-travel switch of small size, a greater tolerance between a positive opening position (POP) and an end-of-travel position (PFC). The distance separating these two positions can therefore be best used by the user to stop a moving body more easily or to absorb its spread out which has traveled beyond the position POP.
2. Discussion of the Background
A fast-action make-and-break switch that can be used as an end-of-travel switch is known, particularly from French patent, FR-A-2 579 009. The use of these switches is subject to standardized constraints. In particular, in addition to having a fast-action make-and-break mechanism, these switches have to be fitted with a positive opening mechanism to avoid defective operation of the switch when actuated as a result of a contact that has to be disconnected becoming stuck. The principle is as follows. For action exerted on an operating plunger, at the start, moving equipment internal to the switch disconnects contacts which are normally closed (known as normally closed contacts). Thereafter, the fact of continuing to depress the plunger causes a change in state of a lever tasked with separating a conducting element from contacts on which it was resting, if this separation could not occur beforehand. This positive opening has to be capable of detaching the conducting element from the contacts. The xe2x80x9cstickingxe2x80x9d concerned is that which may have resulted from welding through the passage of a (standardized) short-circuit current of one thousand amperes. What this means is that the rocking mechanism and the lever are very robust in order to perform this unsticking. Under normal circumstances, of course, such unsticking is not needed because the switch will have performed the expected fast-action breaking.
Under normal circumstances, after the expected breaking, the rocking of the lever of the positive opening mechanism tends to bring the latter closer to the normally closed moving conducting element which has been separated. This mechanism has a detrimental consequence. While having its usefulness, it does nonetheless restrict the possibility of continuing to depress the plunger after the lever has come into contact with the conducting element that it has to separate, in addition to the natural separation. What happens is that, if action continues to be exerted on the plunger, the moving equipment becomes crushed and damage is therefore done to the end-of-travel switch.
With a view to obtaining a greater distance between the opening of the contacts for electrical isolation purposes, the aforementioned French patent envisions associating a conducting element with the moving equipment via a set of compensating springs. By taking this approach, the force exerted by the lever would be in a direction in which the moving equipment would tolerate deformation. This being the case, the tolerance on fitting adjustment between a positive opening point POP and an end-of-travel limit PFC is extended typically from a value of 0.5 mm to 1 mm. In other words, with this mechanism, the fitting tolerance or range of use of the fast-action end-of-travel switch is markedly improved.
However, it remains the case that, for a total travel of 5 mm, the depression distance separating a point of action PA, in which the moving equipment rocks, from the positive opening point POP is still great, and of the order of 2 mm. This means that, with such a mechanism, normal initiated opening will occur for a given position PA, whereas positive opening will not occur until the plunger has been pushed in 2 mm further. This difference is annoying to a user. What the user actually wants is, for normal operation or positive operation (and in this case even with slow opening), for the opening of the contact to occur for one and the same depressed position of the switch plunger. Alternatively, if this is not possible, he wants opening to occur at positions which are truly very close together. In practice, in the invention, it will be shown that a precision of the order of 1 mm can be obtained, which is far better than the previous 2 mm.
In order to overcome this problem, the solution of the invention consists in causing the positive opening action, and the deformation of the moving equipment, to be exerted on one and the same conducting element, the normally closed conducting element, the one at the front of this moving equipment. It will actually be shown that, for the same overall switch size, a greater tolerance can be achieved using the invention. The distance separating the positive opening point from the end-of-travel position will be greater with the invention than in the cited prior art.
A subject of the invention is therefore a fast-action make-and-break switch comprising
a casing fitted with four electrical contacts, facing each other in pairs,
inside this casing, moving equipment carrying along, at each end of its movement, a rear conducting element and a front conducting element, these elements being brought respectively and alternately into contact with two first or two second corresponding opposing contacts,
a set of compression springs resting against this moving equipment and against one end of a plunger for operating the switch,
a rocking control connected mechanically to the plunger and capable of exerting positive action on the front conducting element when the plunger is in a pushed forward position,
a set of compensating springs inserted between the moving equipment and one contact element,
a housing in a plane of the moving equipment to accommodate the set of compensating springs,
characterized in that
this housing is located on the same side as the front conducting element.